#include <iostream>
using namespace std;

const double PI = 3.14;

class Circle
{
 public:



  double r;
  


  double lenth()
  {
    return PI * 2 * r;
  }

};
class student
{
public:

  string Name;
  int ID;

public:
  void showstudent()
  {
    cout << "姓名: " <<  Name  << " 学号: " << ID <<  endl;
  }
  void setname(string _Name)
  {
    Name = _Name;
  }
  void setid(int _ID)
  {
    ID = _ID;
  }


};
int main()
{
  Circle c1;
  c1.r = 10.0;
  cout << c1.lenth() << endl;
  student s1;
  //s1.Name = "张三";
  //s1.ID = 123456;
  s1.setname("张三");
  s1.setid(123456);
  s1.showstudent();
  
  return 0;
}

